The idea of an engine operating on solid fuel, such as a coal fueled diesel engine, was examined as far back as 1900 by Rudolph Diesel. The handling of solid fuels and problems of ash deposition, however, discouraged Diesel from further pursuit of the idea. Between the early 1900's and the end of World War II, thousands of hours of intense research and development were spent trying to develop a practical solid fuel-burning engine. Several of such systems were produced such as one capable of burning coal-water slurry fuels as disclosed in U.S. Pat. No. 4,558,664 issued to Robben or one capable of burning solvent refined coal as disclosed in U.S. Pat. No. 3,965,870 issued to Clark. None of the systems developed however have yet satisfactorily solved the inherent problems associated with solid fuel burning such as fuel handling, ash deposition, high particulate content in emissions, low thermal efficiency, high wear and higher costs associated with the production of special fuels.
Much technological research has also been spent in the development of the natural gas engine. The earliest gas engines were carburetted and spark ignited. Then the short lived "dual fuel engine" was developed whereby a lean mixture of natural gas was ignited by a diesel pilot. However, the expensive diesel pilot injection and the need for carrying two different fuels were soon replaced by a spark plug. Today, most of the natural gas engines are still carburetted and spark ignited with low inherent cycle efficiency and a short-lived spark plug. Only recently, high pressure gas injection into a high compression ratio engine has come under investigation. Such engines are either spark-ignited or diesel pilot-ignited during the high pressure gas injection period.
One aspect of this invention involves ignition of an air-fuel mixture through rapid heat transfer at a high temperature to the air-fuel mixture from a specially designed heat storage unit. Heretofore, insulation of various sections of the engine or use of materials having low thermal conductivity have been suggested and tried in order to enhance the performance and efficiency of the spark-ignited or diesel engine. A variety of such applications are disclosed in the following U.S. Pats. Nos.:
______________________________________ 4,300,497 Webber 4,511,612 Huther 3,110,292 Dobrosavljevic 3,140,697 Peras 4,522,171 Dworak, et al. 2,739,578 Stump 3,259,116 Bricout 1,798,260 Hehr 4,558,664 Robben 4,485,778 Oliver ______________________________________
Although increased performance in some of the important engine output parameters was realized, data in others was still unsatisfactory, such as a high particle content (soot) due to inefficient or incomplete fuel burning and the need for high compression ratios. Likewise, innovations in either solid fule-burning engines or natural gas engines have still not produced a fuel burning system which meets the desired goals such as high thermal efficiency and low pollution content.